If you’re in stop-and-go traffic, you’re probably pretty unhappy about it. If you’re a male penguin balancing an egg on your feet in the freezing Antarctic, that traffic jam is probably keeping you alive.
Scientists studying huddles of emperor penguins in Antarctica have discovered that waves of movement travel through huddled masses of the flightless birds rather like cars creeping on the freeway during rush hour – but in ways that maximize the huddle’s density and keep the birds warm as they incubate their eggs.
Emperor penguins are the only vertebrate species that breeds during the Antarctic winter, and they face freezing winds that blow as fast as 124 mph in an icy landscape that can be as cold as 58 degrees below zero. So they huddle together against the harsh elements – and together, their bodies can raise the temperature within two hours to as high as 98.6 degrees.
At first glance, the penguins may not appear to move much. The males probably can’t run anywhere in a rush, in any case: The fathers-to-be cover their eggs with feathered skin known as a brood pouch, with the eggs resting on top of their feet.
“If you look at a penguin huddle in real time, you hardly see any movement at all – they are all standing very still,” said Richard Gerum, a physicist at the University of Erlangen-Nuremberg in Germany and first author of a study published in the New Journal of Physics.
But watch this huddle of shuffling penguins long enough, and there emerge distinct waves of motion through the feathered masses as one penguin takes a step and the rest follow. It’s a way of maintaining order – something humans have trouble doing, Gerum pointed out.
“When a big human crowd is together, there can be accidents,” Gerum said. “And this is something that never happens in a penguin huddle.”
To understand how these waves begin and behave, the scientists analyzed video footage gathered on penguin colonies near the French and German research bases on Antarctica. Just like cars do in a traffic jam, the penguins would move to fill in an empty space. But unlike cars in a traffic jam, any penguin can initiate movement, whether they’re in the front, to the back or to the side. (A car trying to “initiate movement” from the back would rear-end the car in front of it.)
The waves, said a previous study, travel through the huddle at regular intervals of 35 to 55 seconds. The new study found that whenever a penguin moved a threshold distance of about 2 centimeters (less than an inch), it triggered one of these traveling waves.
The 2-centimeter threshold is no accident: That’s roughly twice the thickness of a penguin’s properly fluffed layer of insulating feathers.
“This suggests that the penguins touch each other only slightly when standing in a huddle, without compressing the feather layer so as to maximize the huddle density without compromising their own insulation,” the study authors wrote.
So if a penguin moves too far away – allowing heat to escape – the penguin next to it moves closer. But if a penguin moves too close to another – crushing its neighbor’s insulating layer of feathers – this will also cause the neighbor to move.
Any penguin can start these waves, and they’re a product of a simple set of rules governing the space between each penguin and its immediate neighbors. And yet, these tiny movements can add up to a large-scale, complex order – akin to the impressive patterns seen in schooling fish, flocks of birds or swarms of ants.